Prior results from this laboratory have shown that elicitors of a plant's defense response bind to receptors on the plant cell surface and within 0-8 minutes stimulate a burst of hydrogen peroxide. This sudden production of hydrogen peroxide serves not only to destroy certain pathogenic compounds but may also stiimulate subsequent phytoalexin production. The next goals of this research are to characterize the oxidative burst, determine its role in triggering phytoalexin biosynthesis, evaluate whether other defense compounds are induced by the oxidative burst, and identify the enzymes and substrates involved in its synthesis. Recent results also indicate that the elicitor molecule is internalized via endocytosis following association with its receptor on the plant cell surface. In further experiments, the kinetics of internalization of the receptor will be examined, and its path will be monitored as it moves from the cell surface to its final intracellular destination . Whether receptors for different elicitors follow identical pathways will also be evaluated. Finally, it has been found that plant cells have receptors for biotin and that macromolecules can be delivered into a living plant cell via biotin receptor-mediated endocytosis if the macromolecules are first covalently derivatized with biotin. The use of this pathway to deliver enzymes, nucleic acids, toxins and antibodies, etc into living plant cells will be explored. Just as higher animals have well developed immune responses to defend against pathogens, higher plants also have defense responses that allow them to resist invasion and damage. The mechanisms by which plant defense responses are regulated is a very important fundamental problem about which, thus far, little is known. With prior NSF support, Drs. Low and Heinstein discovered that exposure of soybean cells to a chemical trigger ("elicitor") of a defense response is followed very quickly by production of hydrogen peroxide by the plant cells. The further goals of this research are to clarify the role of hydrogen peroxide in the defense response, and to pursue other leads concerning the sequence of events between exposure of a plant to a potential pathogen and the production by the plant of protective chemicals. The results of this project should contribute to our understanding of the cellular signaling mechanisms that regulate plant defense responses.
